Device for controlling glare in luminaire



April 20, 1965 K. FRANCK 3,179,797

DEVICE FOR CONTROLLING GLARE IN LUMINAIRE P/a/e A27 Ai Filed Jan. 2, 1962 lea 94d INVENTOR A z/PT EPA/var ATTORNEY S United States Patent 3,179,797 DEVICE FOR CONTROLLING GLARE IN LUMINAIRE Kurt Franck, Newark, Ohio, assignor to Holophane Company, Inc., New York, N.Y., a corporation of Delaware Filed Jan. 2, 1962, Ser. No. 163,444

2 Claims. (Cl. 240-106) This invention relates to the luminaire art and is directed to high angle glare control by prismatic means in lens elements used with extended light sources.

In the prior art, prismatic louvers are used for directing high angle light into lower non-glare angles. Generally,

these louvers are disposed longitudinally and/or trans versely of an extended light source and are disposed to intercept light at high angles and to direct the same downwardly into a predetermined light pattern. Usually, the louvers are provided with a plurality of prisms to carry out light depressing functions. As a result, there is a loss of efliciency as troublesome light rays emerge from the intermediate surfaces of the prisms. For proper efficiency, these rays, too, should be directed into a desired illumination pattern.

The object of this invention is to provide prismatic means which eliminate the use of the louvers of the prior art, including the provision of the plurality prisms with their intermediate surfaces, in favor of single prism formations dimensioned, shaped and disposed for controlling light and directing the same into non-glare angles.

Further objects of the invention ,will become evident upon a reading of 'the following specification, specific embodiments thereof when taken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are representational end views of prior-art prismatic louvers;

FIG. 2 is a representational end view of prismatic means according to the invention;

FIG. 3 is a representational perspective view of the prismatic formations of the invention being disposed for both longitudinal and transverse light control relative to a linear light source;

FIG. 4 illustrates a representational end view of another embodiment of the invention;

FIG. 5 is a perspective view illustrating a mounting arrangement for prism elements of the invention; and

FIG. 6 is a representational elevational view of the light transmitter of FIG. 3, shown in combination with a linear light source.

Referring now to FIGS. 1A and'lB, refractors A and B are provided with prismatic louvers of the single vertical leg type 10, as shown with reference to refractor A, and of the V-shape type 11, as shown with reference to refractor B. The prism formations 12 and 13 on these two different types of louvers are disposed for directing light into a desired light pattern such as is indicated by arrows R and R respectively.

However, intermediate surfaces of these prisms, such as adjacent the apices and valleys thereof, cause troublesome rays of light, which do not strike the refracting surfaces of the prisms, to be directed into angles above the light pattern, and which, when viewed from the direction opposite to the direction of travel will cause glare to the viewer.

In accordance with the invention, such intermediate surfaces are eliminated.

Referring to FIG. 2, there is shown two elongated prisms 20 (elongated in the direction away from the viewer) transversely disposed relative to and underlying a linear light source L, as in FIG. 6. The prisms 20 have slightly rounded sides 21 extending upwardly from and converging above the base 22 of the prisms 21. As shown by the light rays R3-R7, the prisms 20 are laid out for 50 degree shielding, but, of course, could be shallower for shielding at higher angles. This type of arrangement may permit light emanating from the light source L in transverse directions, to strike the base at the angles which would result in their being refracted into glare angles. In such a case, the bottom surface could be covered with cut-off prisms or longitudinal control prisms (prisms for controlling light longitudinally of the prism, in the embodiment shown) or even degree reflecting prisms. Also, the bottom surface may have a contour other than fiat or straight to eliminate such troublesome rays, and longitudinal rows of prisms 31 and 33, respectively, as shown in FIG. 3. With such an arrangement, the grid will afford both longitudinal and transverse light control.

Where transverse control is important, it is also possible to use a sandwich arrangement, as shown in FIG. 4. in FIG. 4, the prisms 40 are shown formed as vertical extensions from a transparent base 46. Additional prisms for transverse control such as prism 47 extend longitudinally of the light source, not shown in FIG. 4, and downwardly from cover 48. Base 46 and cover 48 sandwich the curved prisms 40 between them and provide longitudinal and transverse control of the light, while gaining the additional advantage of having the top and bottom surfaces of the refractor smooth.

FIG. 5 illustrates means by which prisms 50 of the in vention may be mounted to obviate the problems attend ant with the molding thereof because of the sharp-pointed upper edges of the prisms. The prisms 59 shown are mounted on a vertical rail surface 56. As shown, the spaces between the prisms may be left open or they may be covered at the top and/or bottom by plates, either plain or prismatic. Now it will be seen that the curved sided, triangular prisms of the invention eliminate the intermediate prism surfaces of prior art prismatic louvers and obtains more eiiicient light diffusion substantially without glare. v

Although a number of embodiments of the invention have been described, many modifications thereof will be obvious to one skilled in the art and it is intended that the invention is not limited except as defined in the following claims.

What is claimed is:

1. In a luminaire having an elongated light source, a light diffuser comprised completely of a plurality of elongated parallel prisms lying in flat horizontal planes and extending beneath and transversely of said elongated light source, each of said prisms in transverse section having a base and two curved surfaces converging upwardly from said base and toward said light source and being symmetrical on either side of a plane through the apex thereof, each curved surface of each of said prisms receiving downward components of light from said light source between predetermined downward angle refracting substantially all of said light downwardly at a predetermined angle relative to nadir, said predetermined angle relative to nadir corresponding substantially to the lowest 3 angle of said predetermined angles between which said curved surfaces receive said light.

2. In a luminaire having an elongated light source, a light diffuser comprised completely of a base, two crisscrossed sets of a plurality of elongated parallel prisms lying in fiat horizontal planes above said base and eX- tending beneath and longitudinally and transversely of said elongated light source, each of said prisms in transverse section having a base and two curved surfaces converging upwardly from said base and toward said light 10 2 175 0 7 source and being symmetrical on either side of a vertical plane therethrough, each curved surface of each of said prisms receiving downward components of' light from said light source between predetermined downward angles refracting substantially all of said light downwardly at a predetermined angle relative to nadir, said predetermined References Cited in the file of this patent UNITED STATES PATENTS 595,273 Soper Dec. 7, 1897 Rolph Oct. 3, 1939 2,745,001 Guth May 8, 1956 2,904,673 Guth Sept. 15, 1959 2,927,200 Guth Mar. 1, 1960 3,024,355 Sipscomb Mar. 6, 1962 15 3,093,323 Guth June 11, 1963 

1. IN A LUMINAIRE HAVING AN ELONGATED LIGHT SOURCE, A LIGHT DIFFUSER COMPRISED COMPLETELY OF A PLURALITY OF ELONGATED PARALLEL PRISMS LYING IN FLAT HORIZONTAL PLANES AND EXTENDING BENEATH AND TRANSVERSELY OF SAID ELONGATED LIGHT SOURCE, EACH OF SAID PRISMS IN TRANSVERSE SECTION HAVING A BASE AND TWO CURVED SURFACE CONVERGING UPWARDLY FROM SAID BASE AND TOWARD SAID LIGHT SOURCE AND BEING SYMMETRICAL ON EITHER SIDE OF A PLANE THROUGH THE APEX THEREOF, EACH CURVED SURFACE OF EACH OF SAID PRISMS RECEIVING DOWNWARD COMPONENTS OF LIGHT FROM SAID LIGHT SOURCE BETWEEN PREDETERMINED DOWNWARD ANGLE REFRACTING SUBSTANTIALLY ALL OF SAID LIGHT DOWNWARDLY AT APREDETERMINED ANGLE RELATIVE TO NADIR, SAID PREDETERMINED ANGLE RELATIVE TO NADIR CORRESPONDING SUBSTANTIALLY TO THE LOWEST ANGLE OF SAID PREDETERMINED ANGLES BETWEEN WHICH SAID CURVED SURFACES RECEIVE SAID LIGHT. 